Marmosets Have Human-Like Ear for Melodic Pitch

Marmosets can distinguish between high and low notes -- the sound quality of pitch, a key to music and vocalization -- just as humans do, says new research that may call into question just when pitch perception evolved.

A new study recently published in the journal Proceedings of the National Academy of Sciences by researchers from Johns Hopkins University School of Medicine details behavioral evidence showing that the small monkeys use auditory cues to perceive pitch in the same way humans do.

"Until now," lead researcher Xiaoqin Wang said in a release, "we didn't think any animal species, including monkeys, perceived it the way we do. Now we know that marmosets, and likely other primate ancestors, do."

About 10 years ago, Wang found a region in the marmoset brain that appeared to process pitch, the same region where human brains showed pitch processing activity. But he lacked behavioral evidence showing that the animal perceived it as we do. Now, years and a new battery of tests later, he thinks he's found just that.

Wang and his study colleagues administered hearing tests to a group of marmosets that had been trained to lick a waterspout only after they hear a change in pitch.

The tests were designed to spot human-like pitch processing. According to the researchers, while other animals had been observed perceiving pitch, none duplicated three features that distinguish human pitch perception:

Better distinguishing of low-frequency pitch differences than high The ability to distinguish subtle shifts in pitch at low frequencies Perception of pitch differences of simultaneous tones played at high frequencies is related to sensitivity to rhythm After testing the animals, Wang and his team concluded that marmosets had those three qualities in their pitch-perception bag of tricks.

The discovery suggested that the human components for pitch perception may have evolved much earlier than previously thought. Marmosets, very vocal and social animals, are native to South America, and the ancient monkeys were on-board when their home continent split from pre-human Africa some 40 million years ago.

"In addition to the evolutionary implications of this discovery," said Wang, "I'm looking forward to what we will be able to learn about human pitch perception now that we have a primate relative we can study behaviorally and physiologically."

"Now," he added, "we can explore questions about what goes wrong in people who are tone deaf and whether perfect pitch is an inherited or learned trait."

The most comprehensive guide to primates, released this week, names the "five funniest faces" in the monkey world. The massive guide, "Handbook of the Mammals of the World" (Lynx Edicions, 2013), contains information on the 16 families, 77 genera, 479 species and 681 taxa of primates.

Number one on the book's list of funniest faced monkeys is the emperor tamarin. Editors Russell Mittermeier, Anthony Rylands and Don Wilson mention that this monkey was "named after Emperor Franz Joseph of Austria." Members of the species "have a white curved 'mustache' hanging down as far as their chest." The mustache is thought to aid in visual communication.

The researchers mention that bearded sakis "display an extraordinary beard and bouffant hairstyle." Five species have this unique look, all classified in the genus Chiropotes. The one shown here is Uta Hick's bearded saki, native to Brazil.

Black-and-white colobus monkeys "always look disgruntled," according to the editors. That's just the way they look, although they have plenty to be perturbed about.

These plant-eaters are prey for many forest predators, including humans. They have also suffered due to logging practices and habitat destruction. This individual appears to have been captured in a particularly non-cranky moment, nibbling on a leaf.